Automatic backup of ISPConfig server

I'm running a web/email server using ispconfig2 on ubuntu 8.10 (server A). I followed the perfect server guide here. I have another server running ubuntu 8.04 (server B) that i set up using the same guide. I want server B to be an exact mirror of server A so that if server A crashes, I can just plug up B.

What I need to know is exactly what needs to be copied from A to B. Looking at this post on migrating servers, I think the following will work:

On server B:

Use rsync to sync /var/www on B with /var/www on A.

Use rsync to copy Vhosts_ispconfig.conf, /etc/postfix/local-host-names, /etc/postfix/virtusertable, named.conf, and all the pri.* zone files from server A to B.

Use perl to replace server A's local ip address and fqdn with server B's local ip and fqdn in all the files copied over from previous step.

Use mysqldump and rysnc to sync db on server A with db on B.

Now here is where i get stuck. The users and groups in /etc/shadow, /etc/passwd, and /etc/group need to be updated on server B. Can I copy these files from server A to B, or is that going to cause problems on server B? The idea is to write a bash script that does everything and is called from a crontab, so I can't manually open these files and add the lines that don't exist on server B.